The invention relates to a high-pressure gas-heating device with a pressurized container (1) carrying a gas, a heating element (3) arranged in the pressurized container (1), and an insulation (2), which is arranged on the interior wall of the pressurized container (1). In particular, the invention relates to a high-pressure gas-heating device for a coating device for substrate materials with a pressurized container carrying a gas, a heating element arranged in the pressurized container, and an insulation.
During cold gas spraying or kinetic spraying, powder particles measuring 1 μm to 100 μm, and most recently particles measuring up to 250 μm, are accelerated in a gas stream to velocities of 200 m/s to 1600 m/s, without melting on or open, and sprayed onto the surface to be coated, the substrate. Only after a collision with the substrate does the plastic deformation accompanied by very high expansion rates increase the temperature on the colliding interfaces, causing the powder materials to become welded with the substrate and each other. However, a minimum collision rate must be exceeded to this end, the so-called critical velocity. The mechanism and quality of welding is comparable to explosive welding. Heating the process gas increases the sound velocity of the gas, and hence the flow rate of the gas in the die, and thus the particle velocity during a collision. In addition, the particle temperature increases when colliding with the process gas temperature. This results in a thermal softening and ductilizing the spraying material, which lowers the critical velocity of the colliding particles. The rise in process gas temperature hence increases both the particle velocity and particle temperature during collision. Both have a positive effect on the application efficiency and coating quality. The process gas temperature here always stays below the melting point of the used spraying material. Therefore, the cold gas spraying process involves the use of a “colder” gas by comparison to other spraying procedures in which the powder particles are melted by the gas. As is the case in spraying processes where auxiliary materials are melted open by hot gas, the gas must consequently be heated during cold gas spraying as well.
Gas with a high pressure is necessary for accelerating powder particles, in particular coarser particles 25 to 100 μm and larger, up to 250 μm thick. For heating purposes, the gas can be passed through a pressurized container incorporating a heating element. The pressurized container is hence exposed to high temperatures and pressures from the inside. If the temperature is allowed to directly act on the pressurized container, expensive high-temperature materials that are difficult to process must be used, or the size and necessary wall thickness make the pressurized container relatively heavy. A heater with such a pressurized container is difficult to operate owing to the high weight, and has a high thermal inertia. Heat dissipation via the pressure container leads to losses in heating capacity.
Known from DE 197 56 594 A1 is a device for coating substrate materials via thermal spraying, which can be used to spray powder particles. The substrate material coating device comprises a gas-heating device, which takes the form of an electrical resistance heater in one embodiment. The gas-heating device is here situated after a gas buffer container. Also known from the publication is to insulate lines carrying hot gas.
However, the disadvantage to this prior art is that the gas-heating device requires a pressurized container, which is relatively heavy due to its temperature resistance, and in cases when secured to a spray pistol, gets in the way during spray pistol operation. The necessary large material thickness of the pressurized container also makes it thermally inert.
FR 2568672 describes a gas heating method in which the gas is heated in a container with internal insulation. U.S. Pat. No. 5,963,709 discloses a wind heater, which has internal insulation, and incorporates a porous foamed ceramic in front and in back of the heating element, ensuring that the gas stays in the area of the heating element for a sufficient period of time.